Polymer particles refer to particles composed of a polymer or polymers and typically particles having various diameters ranging from dozens of nanometers to dozens of hundreds of micrometers in size. Unlike molded polymer articles such as films, fibers, injection-molded articles, or extrusion-molded articles, polymer particles have a larger specific surface and, by making good use of this and the structure of the particle, the polymer particle has been utilized for proper modification and improvement of various materials. Examples of major applications include modifiers for cosmetics, additives for toners, rheology modifiers such as coating materials, products for medical diagnostic tests, and additives to molded products such as automobile materials and building materials. In particular, by taking advantage of their particle structure, the polymer particles have recently been used as a raw material for rapid prototyping or rapid manufacturing which is a technique used to produce a made-to-order molded product in conjunction with a laser-processing technique.
More recently, there is a need for the polymer particles to have high heat resistance, high solvent resistance, and more uniform particle diameter distribution.
What is known thus far is a method of producing polymer particles comprising dissolving two kinds of polymers in an organic solvent and bringing emulsions composed of each phase into contact with a poor solvent to allow polymer particles to be formed (WO 2009/142231).
That method is characterized in that the diameter of the emulsion is readily adjusted and, in addition, the particle diameter distribution is narrow. At the same time, the method is an effective technique capable of producing a wide variety of polymers into particles, and in particular an effective technique to obtain particles of engineering plastics and high-heat-resistant polymers with a high glass transition temperature and a high melting temperature.
Further, according to Japanese Patent Application Laid-Open Publication No. 2013-177532, polymer particles with uniform particle diameter distribution can be produced even in a larger production scale by controlling the stirring Reynolds number at the time of the emulsion formation.
What is known in those techniques is that a stir condition, a temperature condition, and the like upon precipitation of particles are required to be controlled to stabilize the average particle diameter in each batch.
Meanwhile, a method of mixing a silicon compound using a static mixer capable of continuous synthesis is known as a method of producing particles of submicrometers or larger in size, which method can be applicable for a method of continuously synthesizing silica particles (Japanese Patent Application Laid-Open Publication No. 2007-254176).
However, the production methods described in WO 2009/142231 and Japanese Patent Application Laid-Open Publication No. 2013-177532 involve carrying out batch production and the average particle diameter can possibly vary from batch to batch. Further, there is a need for continuous production that makes the production more efficient and enables facilities to be smaller when large scale production is carried out.
It could therefore be helpful to provide a method of producing polymer particles with lower variability in the average particle diameter and a smaller particle diameter distribution index, which method enables efficient mass production.